Like many documentaries about talented people who did important things during amazing times, “An Unlikely Weapon: The Eddie Adams Story” tends to fall into repetitive fawning. That its subject, a Pulitzer Prize-winning photojournalist, was himself an expert portrait maker — of celebrities, politicians, working-class heroes and, most notably, the victims of war — gives the film a lot more to look at, however, than just talking-head testimony by Mr. Adams’s colleagues (Kim Phuc, Gordon Parks) and admirers (Tom Brokaw, Peter Jennings).

Directed by Susan Morgan Cooper, the movie abounds with striking pictures from Mr. Adams’s long career (he died in 2004), but it keeps coming back to the one he snapped on Feb. 1, 1968, in Saigon: a photograph of a Vietcong prisoner being executed on the street, immortalized during the split second before the bullet exited his skull.

One of the most famous images of the 20th century, it was a photo that changed Mr. Adams’s life and possibly the course of the Vietnam War. The strongest material in “An Unlikely Weapon” contemplates the import of that shot, and of photojournalism itself, on the events of its time. The rest charts Mr. Adams’s subsequent career, from duck hunting with Fidel Castro to oceanfront sessions with Penthouse centerfolds, with perfunctory admiration.

AN UNLIKELY WEAPON

The Eddie Adams Story

Opens on Friday in Manhattan.

Produced and directed by Susan Morgan Cooper; narrated by Kiefer Sutherland; director of photography, Isaac Hagy; edited by Mr. Hagy; music by Kyle Eastwood and Michael Stevens; released by Morgan Cooper Productions. At the Quad Cinema, 34 West 13th Street, Greenwich Village. Running time: 1 hour 25 minutes. This film is not rated.